Which of the following expressions are polynomials in one variable and which are not? State reasons for your answer: $y + \frac{2}{y}$

(D) The given expression is $y + \frac{2}{y}$.
This can be rewritten as $y + 2 \cdot y^{-1}$.
$A$ polynomial in one variable is an algebraic expression where the exponent of the variable must be a non-negative integer (a whole number).
In the term $2 \cdot y^{-1}$,the exponent of the variable $y$ is $-1$.
Since $-1$ is not a whole number,the expression $y + \frac{2}{y}$ is not a polynomial.